Radio frequency (RF) power amplifiers are often used in various portable applications, such as, for example, cellular telephones and other wireless devices. In these applications, the RF power amplifiers are designed to operate into an optimal load impedance and are typically coupled to an antenna of the wireless device.
However, under a load mismatch condition, such as, for example, when the antenna of the wireless device approaches objects (e.g., metal structures, human contact, or the like), the load impedance of the RF power amplifier changes and is no longer optimal, and the RF power amplifier may be driven into a non-linear saturation region. The RF power amplifier may also be driven into a non-linear saturation region under a low voltage condition, such as, for example, when the battery of a battery-operated wireless device is discharged.
When a RF power amplifier is driven into the non-linear saturation region, the output signal of the RF power amplifier is clipped, causing severe signal distortion. The non-linear saturation region and this severe signal distortion are undesirable. In addition, the adjacent channel power ratio (ACPR) and error vector magnitude (EVM) linearity and distortion limits are often exceeded when the RF power amplifier is driven into the non-linear saturation region. This is also undesirable.